Transcript Control II: Implementing Control

Control III – Addendum
(But mostly Administration/Logistics/Support)
MTRX 1701: Introduction to Mechatronics
Dr. David K Wood
Lecture #10
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Staff-Student Liason Meeting
• Happened early last week
• Attended by your Reps and Dr David Rye
• There were a few common issues raised, most of which
we intend to address either this year or in following
years.
• If your question was asked but not answered in this
lecture, and you want to know the official response, email either me or your student rep.
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Issue #1: Not enough contact hours; Too
much material for the contact hours.
This course is, in the main, a course about competence in
technical literacy and self-directed research. As such, we
rely more on self-directed learning and out-of-class prep
and study than many of the more laboratory-based
subjects.
For this component of the course, we have a LOT of
material to cover, and it has to be done in time for the
major assignment. You will notice that from this week,
the pace of the lectures will slow down a little, and we
will get onto some detailed case studies.
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Issue #2: Structure around broad topic
area ‘kind of a blur’; No set textbook.
The course outline on CUSP gives an overview of the course, and
we have been following that lecture and assignment schedule
since the start of the year.
Thus far we have never found a textbook which covers the
breadth of material this course considers. There has been
some consideration of writing one specifically for this course.
If anything is ‘blurred’, refer to the contract from lecture one: “I
am willing to help anybody that has attempted to first help
themselves; You are free to ask questions at any time here in
the lectures, in the labs, or via email”. i.e. Help yourselves!!!
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Issue #3: Insufficient advance notice of
assignments; Posting of slides pre-lecture
I have been attempting to stagger the assignment material to give you some
down-time between assignments. It would appear that this has not been
appreciated, so I will issue the Major assignment this week. That way you
can start working on it as soon as (if not before) you have submitted
Assignment 3.
I never post my slides pre-lecture. There are two reasons for this. Firstly, there is
a clear correlation between pre-posting slides and reduced lecture
attendance. Reduced lecture attendance typically leads to increased levels
of plagiarism, either intentional or unintentional, which isn’t good for
anyone and also increased failure rates. Secondly, pre-issuing lecture slides
can result in pre-conceptions about the material being formed, which may
or may not be correct. As you should be aware by now, it is extremely hard
to break a malformed intuition about a situation, so I seek to avoid this
problem arising.
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Learning Outcomes Covered
Today
• Sense – Control – Act
• Problem to Theory to Solution
• Engineering intuition
• Computer control of machinery
• Mechatronic applicability & limits (analysis)
• Systematic approach to
Mechatronic systems design (synthesis)
• System modelling & control approaches
• Independent / creative research & analysis
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Graduate Attributes Covered
Today
1. Research & inquiry skills
2. Communication skills
3. Personal & intellectual autonomy
4. Ethical, social & professional understandings
5. Information literacy
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Quick Review: What do we
know so-far?
Sense
Think
Act
• We know how to design and work with sensors
• We know how to design actuators for a task
• We know some of the approaches for control
All 3 of these stages can be represented
mathematically, and as a functional sequence
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Sense & Act Transfer Functions
• Transfer functions for sense and act stages are
‘trivial’
• Can be based on:
– Physics
– Design
– Signal Conditioning (software or hardware)
• Are typically not based on:
– “I think this will work” / “I think this is right”.....
• Key Method: Start with the physics, figure out the
maths!
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Control Transfer Functions
• Transfer functions are almost entirely arbitrary!!
– Based on ‘common sense’ or ‘intuited understanding’ or simple
logic.
• Why does Bang-Bang work?
• Why does Hysteresis help?
• Why does PID work?
– Why is my gain-set the “best”
• Why is my MPC better than Bang-Bang?
• Control starts from maths, and we then try and make the
physics implement that maths!
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Control Transfer Functions
• Can I therefore make any arbitrary transfer function
my ‘controller’?
• Performance may be terrible, but there is nothing in
the laws of physics to prevent me from doing it!
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Heuristics in Control
• “Heuristic refers to experience-based techniques for
problem solving, learning, and discovery that give a
solution which is not guaranteed to be optimal.[1]”
• Some ‘arbitrary’ rules: (heuristics)
– Change parameters: Gain Scheduling
– Change controllers: Mixed-mode control
– Nest controllers: Multi-level control
• In 99% of cases, in order to generate a ‘perfect’ solution,
the controller will need to be infinitely complex!
• Controller design itself is a heuristic process.
[1]: http://en.wikipedia.org/wiki/Heuristic
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Transfer Functions
• If you can represent it as a transfer function, you can
make it happen.
• The complexity of the implementation may be large,
but is almost always possible (especially in
software/firmware)
• Some transfer functions are driven by physics, but
there are plenty that can drive the other way.
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Sense, Think, Act?
• It forms a good starting point.
• It clearly divides the system components into
actuators, sensors and controllers.
• It has limited fundamental truth!
• If you have a good reason, it can be deviated from!
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Summary
• If I know the equations, I can make it happen.
• My physical “controller” may be performing many
other tasks (filtering/output limiting etc.)
• Appropriate controller selection depends on the
complexity of the equations (and required frequency
of evaluation)
• Don’t be constrained by formulaic models!
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Major Assignment
• “This assignment is about applying what you have
learned in this course to the design of a mechatronic
system. The intention is to get you to think about
what we have studied and to come up with an
original design for a practical system. The design
should be sensible and considered. Emphasis is to be
placed on systems design and the clarity of the
technical description. A quantitative approach
should be adopted.”
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Major Assignment
You have been contracted to design the next generation of
intelligent cruise control system for a major car manufacturer.
The system should include proximity sensors to follow the car infront, monitoring systems to evaluate driving conditions, and
limit peak speed appropriately, and the ability to self-test and
ensure that the car is in a safe state to drive before engaging. This
system is intended to be rolled out across the manufacturer’s
entire range, from small 2-door city hatchbacks to large crew-cab
utilities and high-performance sports vehicles. It should also be
capable of acting as a black-box, recording all relevant
information about internal and external vehicle state in the case of
a crash.
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Major assignment
• Each section has a page limit.
• PAGE LIMITS WILL BE ENFORCED!
• Wherever possible be specific.
– Equations are almost always shorter than sentences!
• Try and keep a uniform level of technical depth
across the entire assignment.
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